This counts instances where the destination address type field, which distinguishes individual versus group SMDS addresses, in a SIP3 PDU header was invalid, one of the address-related validation checks. An admin treats this as a sign of malformed addressing coming from a specific sender, distinct from the address-value checks in lportSmdsCntSip3DaInvalids that follow. For example, if only address-type invalids are climbing while the address-value invalids stay flat, the sending device is likely setting the type-indicator bits incorrectly while otherwise formatting the actual address bytes correctly.